Piezoelectric microphone



. y 17, 1951- P. B. WICKHAM ETAL 2,561,084

PIEZOELECTRIC MICROPHONE Filed May 1, 1946 INVENTORS KER B WICKH PAR SAMUEL A JOHNST Patented July 17, 1951 PIEZOELECTRIC MICROPHONE Parker B. Wickham, Delavan, and Samuel A. Johnston, Walworth, Wis., assignors to The George W. Borg Corporation, Chicago, 111., a

corporation of Delaware Application May 1, 1946, Serial No. 666,284

10 Claims.

the invention is a new and improved device of this character.

As illustrated and described herein, the invention is directed specifically to a microphone adapted for use in a watch timing apparatus for picking up the beats of a watch which is being tested. The invention may, therefore, be regarded as an improvement on the invention disclosed in United States Patent No. 2,175,021, granted October 3, 1939.

The invention will be described hereinafter with reference to the accompanying drawing, in which- Fig. l is a top or plan view of a microphone embodying the invention;

Fig. 2 is a section on the line 22, Fig. l; and

Fig. 3 is a section on the line 33, Fig. 2.

Referring to the drawing, the reference character Ill indicates a case or housing, which may be a casting of zinc alloy or other suitable material. The shape of the housing isclearly shown in the several figures of the drawing, from which it can be seenthat it is of circular formation, with an extension I l at the base, from which there projects the cylindrical neck IZ'.

The neck 12 has an axial opening which conimunicates with the interior of the housing. A tubular shaft 13, only part of which is shown, is threaded into this opening, which is tapped for the purpose, and provides means for rotatably mounting the microphone on the frame or casing of a watch timing machine.

The opening in the top of the housing Ill is circular and is formed with an annular shoulder II on which the microphone assembly is sup ported. This assembly will now be described.

The reference character l indicates a disc of synthetic resin or similar material, which is of the proper size to fit the opening in the top of the housing ID. A relatively thick layer of soft foam rubber is indicated at l6, and a thinner layer of flexible sheet rubber at [1. These parts may be secured together by a suitable cement. The upper layer I! should be made of a sulphur free rubber to avoid any danger of tarnishing There is a central opening extending through suitable cement.

the above described parts and the metal pin 2| is located in this opening. The pin 2| is held in place by a washer l9, secured by the split ring 20. It will be noted that the parts are com pressed somewhat between the head of the pin 2| and the washer I9, as indicated by the indentation of the head of pin 21 in the layers l1 and IS.

The crystal 22 is of known construction and comprises preferably a sheet or plate of Rochelle salt having thin foil electrodes on the opposite sides thereof. The terminal strips 23 and 24 are attached to these electrodes. The crystal with its electrodes is coated in known manner by a layer of suitable varnish or similar compound to prevent the absorption of moisture.

The crystal 22 is mounted in a slot cut in the pin 2| near the end, where it is secured by a This arrangement is shown clearly in Figs. 2 and 3, from which it will be seen that the crystal has no other support.

The reference character 25 indicates a resistor, having the usual terminal wires 26 and 21. This resistor is mounted on the Bakelite disc l5 by means of the screw 2'8, which passes thr-ough'a loop in the terminal wire 26. The terminal wires 26 and 21 are soldered to the terminal strips 23 and 24 of the crystal and since the wires are rather stiff they function effectively to support the ends of the strips 23 and 24, which are thin and flexible. The pin 2| is connected to ter minal wire 26 by means of a flexible lead 30 and the wire 26 is connected to the housing Ill by a wire 3!, a boss 32 being provided for convenience in making a soldered connection between wire 3| and the housing. These connections effectively ground the pin 2| and one of the crystal electrodes to the housing.

The insulated conductor 33 is connected to the terminal wire 2! and extends through the tubular shaft l3 to the tick amplifier of the watch timing apparatus. This conductor affords a connection between the ungrounded electrode of the crystal and the grid of the tube at the first amplifier stage. It may be stated also at this point that the resistor 25 functions as the grid leak for this tube. The end of the tubular shaft I3 is sealed around the conductor 33 by means of wax or other suitable plastic material, as indicated at 35.

In the manufacture of the microphone, the so called microphone assembly, including the 'resistor 25, the crystal 32 and the ground Wire 3!, is completed outside the housing [0. The

' conductor 33 and the wire 3| are long enough so that the former can be soldered to wire 21 and the latter to boss 32" before the microphone assembly is placed in the housing. These connections having been made, the walls of the opening in the housing may be coated with a suitable cement, after which the microphone assembly is inserted as shown in Fig. 2, with the disc 15 resting on the shoulder M.

For the purpose of holding a watch in position on the microphone a spring 36 is provided, said spring being attached to the housing In by means of a screw 31, as shown in Fig. 3. The spring 36 extends upward and over the top of the microphone and at its free end carries a rubber button 38 which is in substantial alignment with the pin 2|. A watch to be tested may be inserted dial up between the head of pin 2| and the button 38, the back of the case resting on the head of the pin, and is retained by the spring. In this connection it may be pointed out that the pin 2| projects only very slightly above the surface of the rubber layer I1 and since layer 16 yields readily the pin is depressed enough when a watch is inserted so that the watch not only contacts the head of the pin but the rubber layer I! also. Thus considerable friction is developed, even if spring 36 has only a moderate amount of tension, and there is no danger of the watch slipping oil when the microphone is rotated as required for testing the watch in different positions.

The microphone disclosed herein may be used with any watch timing machine which requires a means for picking up the watch beats and generating electrical impulses responsive thereto. United States Patents Nos. 2,254,649and 2,303,540 disclose watch timing machines of this type and describe the operations involved in timing watches.

The present invention is concerned only with the microphone and it will suffice therefore to explain its operation in converting the watch beats to electrical impulses. Information as to further details of the timing operation may be obtained from the patents above referred to.

Assuming that a watch has been placed on the :microphone as previously described herein, the

watch case will be in contact with the head of pin 2| and the mechanical shocks produced ,by the beating of the watch will be transmitted to pin 2| and thence to the crystal 22 supported thereon. In this operation the pin 2| vibrates longitudinally, being free to do so because of the resilient support afforded by the soft. rubber layers l6 and 18. Now the crystal 22 has one corner fixed to pin 2| and this corner therefore moves with the pin. Other parts of the crystal move also to a degree but due to the inertia of the crystal a certain amount of bending takes place whereby electrical potentials are developed between the crystal electrodes according to the well known piezo-electric effect. These potentials are transmitted to the tick amplifier where they are amplified to the extent necessary for proper operation of the timing apparatus. Explaining this a little more, the conductor 33, which is connected to one electrode of the crystal, extends to the grid of the tube at the first amplifier stage, while the cathode of the tube is grounded and is connected to the other electrode of the crystal by way of the ground connection to the housing 10.

The crystal may be made somewhat more responsive by loading the corner opposite the pin it, or the adjacent corners, but such loading is not necessary for picking up watch beats, even the beats of the smallest wrist watches, and is protection of Letters Patent is desired will be pointed out in the appended claims.

We claim:

1. In a microphone for picking up watch beats, a cup shaped housing, a multi-layer closure for said housing, said closure having a watch supporting surface and including nonmetallic resilient layers disposed on opposite "sides of a relatively stiff layer, a metallic member extending through said closure and supported by said resilient layers, said member being adapted for engagement by a watch resting on said'surface, -and a piezo-electric crystal mounted on saidmembe'r inside saidihousing.

2. Inamicrophone for picking up 'watch'beats, a cup shaped housing, a multi-layerclosure'forsaid housing comprising a lower main supporting layer, an upper layer of sheet rubber, and a mass of soft foam rubber interposed between said layers, a metallic member extending through said closure, means including said rubber material for resiliently mountingsaid member on said supporting layer for engagment with the case of a watch resting on said upper layer, and a piezoelectric crystal mounted on said member inside said housing.

3. In a microphone for picking up Watch beats. a casing, a cover for said casing, a support tor a watch on said cover, said support including a layer of softrubber, a metallic member extending through said cover and support with the end thereof in position to be engaged by a watch on said support, a layer of soft rubber below said cover, means including said layers for resiliently securing said member to said cover, and a piezoelectric crystal supported on said member inside said casing.

4. In a microphone for picking up watch beats, a support for a watch, said support including a resilient layer of soft rubber or the like material, a relatively rigid supporting member for said layer, a metallic pin extending through said member and layer with the end thereof in position to be engaged by the case of a watch held against said support, mains including said layer for resiliently supporting said pin on'said member, and a piezo-electric crystal supported on said pin beneath said member.

5. In a microphone for picking up watch beats, a support for a watch, said support comprising a relatively stiff main supporting member, a layer of flexible material for engagement by a watch case and a relatively thick layer of soft rubber or the like material intervening between said flexible material and said member, a metallic pin extending through said support with the end thereof in position to be engaged by said watch case, means including said layers and a layer of soft rubber beneath said member for resiliently securing said pin thereto, and a piezo-electric crystal supported on said pin beneath said member}? 6. In a microphone for picking up watch beats,

a casing, a relatively stiii cover for said casing, means including a layer of soft rubber or the like material forming a resilient support for a Watch on the outside of said cover, a metallic pin extending through an opening in said cover and support and having a head larger than said opening adapted to be engaged by a watch on said support, means for resiliently supporting said pin on said cover, and a piezo-electric crystal mounted on said pin inside said casing.

7. In a microphone for picking up Watch beats, a casing, a cover for said casing, a resilient support for a watch on the top of said cover, a pinlike metallic member extending through said cover and support, means for resiliently supporting said member on said cover with one end of said member in position to be engaged by a watch on said support, and a piezo-electric crystal mounted on said member inside said casing and disposed in a plane to which the longitudinal axis of said member is substantially perpendicular, said crystal having an unsupported portion free of mechanical loading and adapted to vibrate due to the inertia of its own mass in response to watch beats transmitted by said member.

8. In a microphone for picking up watch beats, resilent providing a supporting surface for a watch, a metallic member in the form of a rod or pin having one end disposed for engagement by a watch on said surface, means supporting said member for longitudinal vibration responsive to beats of the watch, a piezo-electric crystal disposed in a plane substantially parallel to said surface and having one extremity attached to said member, the remainder of the crystal being unsupported and having sufiicient inertia due to its own mass to cause it to vibrate responsive to vibration of said member, and electrodes for said crystal between which electrical potentials are generated responsive to the vibration of the crystail.

0. In a microphone for pickin up watch beats, a support for a watch, a metallic memberfor transmitting mechanical vibrations, means resiliently supporting said member with a 'part thereof disposed for engagement by a watch on said support, a piezo-electric crystal mounted on and supported exclusively by said member, said crystal being subject to vibrations due to the inertia of its own mass in response to vibration of said member, and electrodes for said crystal be tween which electrical potentials are generated by vibration thereof.

10, A microphone as claimed in claim 9, wherein the crystal is rectangular and is attached at one corner to the metallic member.

PARKER B. WICKHAM. SAMUEL A. JOHNSTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

